This invention relates to the deposition of material layers using acoustically ejected droplets, and more particularly to an acoustic printhead system configured to improve droplet placement on a substrate.
For high-quality printing applications such as photo-finishing, it is desirable to have highly accurate spot placement. For example, drop placement should not be more than a few microns from a desired location. Due to these requirements, there is an incentive to minimize the possible contributions to drop misdirectionality. A first such contribution comes from what is known as a nearest neighbor effect or cross-talk. In an acoustic printhead, this problem exists due to sound emitted from a particular transducer along a row, which diffracts as it propagates in the substrate. Some finite amount of sound energy may, under this construction, end up in a neighboring ejector along the same row. This sound field will be focused by the neighboring lens towards or very near the focal point of the neighboring lens. The acoustic field, due to cross-talk, will have a slightly different phase compared to the main beam due to the difference in propagation paths. It has been observed that under these circumstances (i.e. a main beam and a secondary field with a slightly different phase) the drops come up from the liquid at a slight angle to the main sound beam. This undesirable secondary field causes a misdirectionality which may not be acceptable for high-quality printing, such as for photo-finishing.
Another defect which is undesirable in high-quality printing applications is the failure of even a single acoustic printhead ejector or jet. The failure of a single acoustic printhead ejector, may result in an undesirable printhead signature such as a white line on the printed substrate.
The present invention mitigates the issue of cross-talk between adjacent ejectors and that of severe printhead signatures arising from defective or improperly operating ejectors.
An at least two-pass acoustic printing system uses an acoustic printhead having an array of ejectors arranged in rows and columns. Operation of each ejector is individually controllable. To minimize cross-talk errors a first selected ejector in a selected row is identified as an odd ejector of the selected row. Thereafter a first firing sequence of the first selected ejector is generated based on the first selected ejector being identified as odd. Then a second ejector, immediately adjacent the first ejector, is selected and is identified as an even ejector. Thereafter a second firing sequence is generated for the second selected ejector based on the selector being identified as even. The first and second firing sequences result in the first ejector and the second ejector being active during non-concurrent time periods. When a defective ejector of the array is detected, an operable ejector firing to the same substrate area is determined. A firing sequence from or associated with the defective ejector is transferred to be used by the operable ejector wherein the operable ejector fires both its own firing sequence and the firing sequence of the defective ejector.